Answer:
Acidic Conditions:
Begin by protonating the oxygen in the carbonyl group, in the next step you can add water to the activated nucleophile to make the tetrahedral intermediate. The rest of the reaction are acid base reactions to maintain an acidic equilibrium and end up the ammonium as the acid catalyst.
Basic Conditions:
You may begin by adding the hydroxyl group to the carbonyl carbon and then protonating the now negative oxygen from the previous alkene with the proton left over by the hydroxyl group (originally it was water). You need to dissociate your tetrahedral intermediate by protonating the amide and then pushing it out when you take the proton by the oxygen pushing the electrons to make a double bond to form the carbonyl group and push out the NH3. In the end base deprotonates the carboxylic acid and you wind up with ammonium. The main key is equilibrium, you end up with a negative charged ion at the end because you maintain a negative charge in a basic mechanism.